Currently, the fabrication of field emission emitter of optoelectronic device mainly employs the association of lithography and etching process of the typical semiconductor manufacturing for making the pyramidal emitter. However, this method could not fabricate field emission elements with high aspect ratio, and thus could not provide high field enhancement factor for the field emission emitter implemented in optoelectronic device accordingly. Therefore, it would normally require higher driving voltage for the emitter to trigger the electrons. Some relevant researches employed the high aspect ratio nano-structure as the field emitter, such as carbon nanotubes or other semiconductor nanorods, so it could reduce the driving voltage because of providing high field enhancement factor. However, for the fabrication of these material, they comprise step of growing process under high temperature (>500° C.), so they are not easily integrated into the semiconductor process. Simultaneously, they lack of sufficient uniformity reaction for large area production, and are not suitable for the fabrication of large-scale device.
For example, the Taiwanese Patent No. 1,248,626 discloses the use of carbon nanotubes as the emitter of field emission device, wherein the fabrication method comprises firstly growing a catalyst metal layer, such as Fe, Co, Ni on a substrate; then, introducing a carbon source gas and heating to about 700° C. of reaction temperature; and producing the carbon nanotubes array as the cathode electrode in the presence of catalyst. The problems of prior art at least include: employing high pollution metals, such as Fe, Co, Ni, in the semiconductor process, wherein these metals are easy to make the control device failed and to contaminate the processing pipes; and increasing the processing cost due to high reaction temperature.
Thus, in order to acquire the high aspect ratio nano-structure as the field emitter but avoid the disadvantages of high processing temperature (>500° C.), the ZnO nanowires are fabricated by the low temperature processing technology in this invention. Particularly, the ZnO based field emission emitter capable of exhibiting excellent emission efficiency at room temperature now becomes more important. On the other hand, if employing the carbon tubes or one-dimensional nanorods in a non-oxide system, they will frequently react with the gas in the field emission device at the same time when electrons trigger, so as to damage the field emission device during operation. Moreover, in the ordinary processing for field emission device, the aspect ratio for the emitter material is constricted after fabrication, there is less possibility to improve the field emission characteristics.